Abstract: As the environmental protection requirements for surrounding sea areas of Tongming Strait are high, the crossing strata are complex and changeable, the underground fresh water and sea water appear alternately, the crossing section is long with large friction, the stratum is loose, and it is difficult to maintain the stability of borehole, which is very easy to cause drilling problems such as drilling fluid over-spilling, variation of drilling fluid performance, bit balling and lost circulation, et al. In view of the above problems, environment-friendly shale inhibitor, salt-resistant filtrate reducer and lubricant were selected by research, and on this basis, an environment-friendly wellbore stabilizing drilling fluid system was formed for the very-shallow strata, which has excellent performances of shale inhibition, lubrication, solid contamination resistance and wellbore stability. Application of the system in directional crossing project of Tongming Strait shows that, the performance of the drilling fluid is stable with good lubrication effect, capable of effectively reducing the pump pressure and friction resistance, and the wellbore stability is strong with no complex drilling accidents occurring, so that the directional drilling cycle is shortened by 87 days, which provides a reliable guarantee for smooth pipe dragging.